SDM-USB-QS-S USB MODULE DESIGN GUIDE
„ 0.812" „
1 LOT 10000
o.i 25" r.
The Linx QS Series USB module allows the rapid
addition of USB to virtually any device. Housed in
a compact SMD package the QS module
provides a complete solution for converting
between USB and logic level serial sources. The
module can be directly connected to virtually any
serial device including microprocessors,
RS232/RS485 level converters, or Linx wireless
RF modules. The QS module is completely self
contained and requires no external components,
(except a USB jack) and includes all necessary
firmware and drivers, freeing the designer from
complicated programming. Power can be
supplied externally or from the USB bus. Both Figure 1: Package Dimensions
USB 1 .1 and USB 2.0 are supported at data rates
■ VID, PID, Serial Number, and
Descriptors Programmed via USB
■ No External Components Needed
(Except a USB Jack)
■ Compact Surface-mount Package
■ Drivers and Firmware Included
■ Supports Windows 98/2000/ME/XP
■ USB 1 .1 and 2.0 Compatible
■ Single Chip I
Serial Data Conversion
■ 3Mbps baud rate
■ Supports Low-Speed USB
■ Full Handshaking Support for
RS232 and RS485
■ Bus-or-Self Powered
■ Interface / Upgrade Legacy Peripherals
■ Interfacing Microcontrollers To USB
■ USB-to-RS232 / RS485 Converters
■ Interfacing RF Modules To USB
■ USB Smart Card Readers
■ USB Modems
■ USB Instrumentation
■ USB Game Controllers
■ USB-to-Serial Converter Cables
Master Development Kit
ABSOLUTE MAXIMUM RATINGS
Supply voltage Vqq
Max Current Sourced By Data Pins
Max Current Sunk By Data Pins
+225°C for 10 seconds
Any input or output Pin
V cc + 0.5 VDC
•NOTE* Exceeding any of the limits of this section may
lead to permanent
damage to the device. Furthermore, extended operation at these maximum
ratings may reduce the life of this device
:■ ■ .0
v C c
Single Ended RX Threshold
Differential Common Mode
Differential Input Sensitivity
o ; ' a
Operating Temperature Range
This product incorporates numerous static-sensitive components.
Always wear an ESD wrist strap and observe proper ESD handling
procedures when working with this device. Failure to observe this
precaution may result in module damage or failure.
USB data signal plus.
USB data signal minus.
Positive power supply.
Goes low during USB Suspend Mode. This pin can be used to
power down external logic when the host puts the USB bus
into suspend mode.
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bus. This allows for the connection of a LED indicator.
Transmit enable line for RS485 applications.
Data Terminal Ready control / handshake output
Clear To Send control / handshake input
Request To Send control / handshake output
Transmit asynchronous data output
Receive asynchronous data input
Data Set Ready control / handshake input
Data Carrier Detect control / input
Ring Indicator control input
The QS modules are packaged in a hybrid SMD package that supports hand or
automated assembly techniques. Since QS modules contain discrete
components internally, the assembly procedures are critical to ensuring the
reliable function of the QS product. The following procedures should be reviewed
with and practiced by all assembly personnel.
The following pad layout diagram is designed to facilitate both hand and
automated assembly .
The QS module's primary mounting surface is sixteen pads located on the bottom of
the module. Since these pads are inaccessible during mounting, castellations that
run up the side of the module have
been provided to facilitate solder
wicking to the module's underside.
This allows for very quick hand
soldering for prototyping and small
If the recommended pad guidelines
have been followed, the pads will
protrude slightly past the edge of the ,
module. Use a fine soldering tip to Ftgure 4: QS Soldering Techmque
heat the board pad and the castellation, then introduce solder to the pad at the
module's edge. The solder will wick underneath the module providing reliable
attachment. Tack one module corner first and then work around the device taking
care not to exceed the times listed below.
Absolute Maximum Solder Times
Hand-Solder Temp. TX +225°C for 10 Seconds
Hand-Solder Temp. RX +225°C for 10 Seconds
Recommended Solder Melting Point +180°C
Reflow Oven: +220°C Max. (See adjoining diagram)
For high-volume assembly most users will want to auto-place the modules. The
modules have been designed to maintain compatibility with reflow processing
techniques, however, due to the their hybrid nature certain aspects of the
assembly process are far more critical than for other component types.
Following are brief discussions of the three primary areas where caution must be
Reflow Temperature Profile
The single most critical stage in the automated assembly process is the reflow
process. The reflow profile below should not be exceeded since excessive
temperatures or transport times during reflow will irreparably damage the modules.
Assembly personnel will need to pay careful attention to the oven's profile to
ensure that it meets the requirements necessary to successfully reflow all
components while still remaining within the limits mandated by the modules
Forced Air Reflow Profile
120 150 180 210 240 270 300 330 360
Time (Seconds) ^
Figure 5: Maximum Reflow Profile
Shock During Reflow Transport
Since some internal module components may reflow along with the components
placed on the board being assembled, it is imperative that the modules not be
subjected to shock or vibration during the time solder is liquid.
The modules are wash resistant, but are not hermetically sealed. Linx
recommends wash-free manufacturing, however, the modules can be subjected
to a wash cycle provided that a drying time is allowed prior to applying electrical
power to the modules. The drying time should be sufficient to allow any moisture
that may have migrated into the module to evaporate, thus eliminating the
potential for shorting damage during power-up or testing. If the wash contains
contaminants, the performance may be adversely affected, even after drying.
The Linx SDM-USB-QS-S module will convert USB signals from a host, such as
a PC or hub, into TTL logic level signals. This enables the module to be
connected directly to microcontrollers (or Linx RF modules for wireless
applications) or to RS232 or RS485 level converters for communication with
legacy devices. The module handles all of the complicated enumeration and bus
communication processes thus freeing the designer to focus on handling the
data. All necessary firmware is included in the module and the device descriptors
can easily be changed to customize the device.
The host application software can access the USB device by simple custom
functions or by standard Windows Win32 API calls. In addition, Virtual Com Port
drivers are available that make the USB module appear to the PC as an
additional COM port without the need for additional system resources, such as
an IRQ or address. This allows the designer to program the application software
to use standard serial or parallel ports and then to simply select the port that
represents the USB module. The drivers will then automatically direct the data to
the USB bus and the device.
INSTALLING THE DRIVERS
The drivers for the USB module are included with the module's
development system or may be downloaded from the Linx web site
(www.linxtechnologies.com). These drivers should be downloaded onto the hard
drive of a PC or onto a disk. When the module is attached to the PC for the first
time Windows will automatically detect the device and search for the best driver.
The user will be prompted to provide a location for Windows to find the drivers,
so the user will then browse to the folder or the disk, click Next and Windows will
do the rest. Windows XP may return an error window shown in the figure below.
f ^ The software you are instating 'orthis hardware.
Unx LTUSB Device
; : hasnct passed Windows Lagoiestngte venfyftsGanoBSibiicy
with Windows: XP. ffel meWre.^'m- is ^nxs 11 ;.-
(Continuing your installation of Ihts software may impair
or destabilize the correct operation of your system
either immediately or in the future. Microsoft strongly
recommends that you stop this 'ink^^ier* now and
contact the hardware vendor for software that has
passed Windows Logo testing.
^ J "
Figure 6: Windows XP Driver Error Window
This window is simply a warning that the driver has not gone through Microsoft's
certification process and could potentially pose a problem for the system. The
drivers provided for the QS module have been independently tested and should
not pose any problems unless modified by the user. Click the Continue Anyway
button to finish the installation process.
THEORY OF OPERATION
Figure 7 below shows a block diagram of the QS module.
Figure 7: SDM-USB-QS-S Block Diagram
The USB transceiver block provides the physical interface for the USB signalling.
The USB DPLL locks onto the NRZ data and provides separate recovered clock
and data signals to the Serial Interface Engine (SIE).
The SIE performs the parallel to serial and serial to parallel conversion, bit-
stuff i ng/u n -stuff i ng , and CRC calculations on the USB data.
The USB Protocol Engine manages the data from the USB control endpoint, the
USB protocol requests from the USB host controller, and the commands for
controlling the functional parameters of the UART.
Data from the USB data out endpoint is stored in the TX buffer and removed from
the buffer to the UART transmit register under control of the UART FIFO
Data from the UART receive register is stored in the RX buffer prior to being
removed by the SIE on a USB request for data from the device data in endpoint.
The UART FIFO controller handles the transfer of data between the RX and TX
buffers and the UART transmit and receive registers.
The UART performs asynchronous 7/8 bit parallel to serial and serial to parallel
conversion of the data on the RS232 (RS422 and RS485) interface. Control
signals supported by the UART include RTS, CTS, DSR , DTR, DCD and Rl. The
UART provides a transmitter enable control signal (485_TX) to assist with
interfacing to RS485 transceivers. The UART supports RTS/CTS, DSR/DTR and
X-On/X-Off handshaking options. Handshaking, where required, is handled in
hardware to ensure fast response times. The UART also supports the RS232
BREAK setting and detection conditions.
POWER SUPPLY GUIDELINES
The USB module can be powered in two ways: from the USB bus or from an
external source. If neccisary, a voltage regulator can be used to supply a clean
5V as the external source, or the VCC pin can be connected to the bus power
pin of the USB connector. Using the bus to power the module is an advantage
because the module then uses power from the host rather than from the
peripheral. This is especially helpful if the peripheral is battery powered. Figure
8 shows the schematic for a bus powered device.
USB Type B
Figure 8: USB Bus Powered Schematic
The USB specification has strict allowances for using power from the bus. A
device is allowed to use 100mA before enumeration, 500mA during normal
operation, and 500|iA in suspend mode. A descriptor stored in the EEPROM will
tell the host how much current the device will pull from the bus so that the host
can allocate the appropriate power. The modules come programmed for 100mA,
but if the final product will draw more than this then the device descriptors will
need to be changed, as described in the next section.
CHANGING THE DEVICE DESCRIPTORS
The QS can be customized to display your product's name, manufacturer name,
and to use different Product Identifiers (PID) and Vendor Identifiers (VID). This
allows an end user to see the final product's name in their Windows Device
Manager and when the hardware is first loaded. The PID and VID are set by the
USB Implementers Forum and should not be changed unless the final product
has gone through the certification process and received its own unique IDs.
The Manufacturer, Description, and Serial Number strings can all be modified
using the Linx Programming Software, which is included in the module's
development system. This easy-to-use software will reprogram the module via
the USB bus and can be done as a part of the final testing procedure.
Once the module is reprogrammed some modifications to the driver files may be
necessary. If a VID and PID other than the default Linx numbers are used these
numbers will need to be added to the files. This requires modifying several lines
in the .inf files and is described in detail in the programmer user manual.
Modifying the name displayed by the Windows Device Manager requires
changing only one line, also described in the programmer user manual.
Note: when these drivers are installed on a system with Windows XP an error message
may be displayed stating that these drivers are not certified and could potentially crash the
system. As long as no other changes are made to the .inf files, this should not be a
There are many potential uses for the QS Series modules, but three will be
described here. Figure 9 shows the QS and a MAX213 RS232 level converter
IC from Maxim. This creates a USB-to-RS232 converter that supports all of the
standard handshaking lines. Similarly, RS485 or RS422 level converter chips
could be used for designs requiring those standards.
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Figure 9: RS232 To USB Converter
The QS Series modules can be used with Linx RF modules to create a wireless
link between two PCs. Figure 10 shows a design using the ES Series RF
modules. One potential feature not shown in the schematic below is that one of
the output lines of the QS module, RTS or [
lines of the RF modules enabling the host to turn the RF modules on and off.
Figure 10: Wireless Modem Using The Linx ES Series RF Modules
TYPICAL APPLICATIONS (CONT)
Figure 11 below shows the QS module connected to a microprocessor. This is
the design used in the QS Master Development Kit and the documentation for
the kit describes the connections and software.
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Figure 11: Interface With A Microprocessor
The host application can access the QS module in two ways. First is through
Virtual COM Port drivers. These drivers make the QS appear as an extra COM
port on the host PC. This allows the application to use standard writes and reads
to a serial port and the drivers will redirect data to the USB device.
Second are a series of custom functions supported by the direct driver .dlls.
These functions are also described in the Programmer's Guide where examples
are given in both Visual Basic and C. The Programmer's guide can be
downloaded from the Linx web site (www.linxtechnologies.com).
In addition to the Programmer's Guide, the QS Master Development Kit (MDEV-
USB-QS) includes example software and sample system source code. This
source code provides the driver function declarations, examples of how to use
the functions in a program, and other code that may be of use.
M l TECHNOLOGIES
IHIII illHIII II II' EM
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The Antenna Factor division of Linx offers
a diverse array of antenna styles, many of
which are optimized for use with our RF
modules. From innovative embeddable
antennas to low-cost whips, domes to
yagi's, and even GPS, Antenna Factor
likely offers or can design an antenna to
meet your requirements.
W£ l/ALUf OF CONNECTIONS
Through its Connector City division, Linx offers a wide
selection of high-quality RF connectors, including FCC-
compliant types such as RP-SMAs that are an ideal
match for our modules and antennas. Connector City
focuses on high-volume OEM requirements, which
allows standard and custom RF connectors to be offered
at a remarkably low cost.
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Linx Technologies is continually striving to improve the quality and function of its products; for
this reason, we reserve the right to make changes without notice. The information contained in
this Data Sheet is believed to be accurate as of the time of publication. Specifications are based
on representative lot samples. Values may vary from lot to lot and are not guaranteed. Linx
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are the trademarks of Linx Technologies, Inc.
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